Beam tube switching circuits



May 28, 1957 \J. R. BETHKE BEAM TUBE swrrcnmc CIRCUITS Filed Aug. 22, 1955 RESET AND CLEAR .m A .TTM H INVENTOR JOHN R. BETHKE D in a. AS 6 N M W S H D ED @Z 0 DW 0% AL Wm T 6 .w T G "a A m H Nw ET2 I. VI 5 EW 0 D F 5L H ODD SWITCHIN G ATTORNE.

dohnR. Eethke Pooh Pa. to ,Gur 9 3 9 2,794,147 BEAM roan swrrcnnsn cine-tins ration, fletroit, aieln, a corporation A nnnmmigust 22., 19 Serial No. 529,661

This invention relates generally to multi-position electron beam position tubes and more particularly to means and methods for clearing and resetting the beam to a 6" position in a maid-position electron beam position tube circuit.

In recent years there has been developed a tube having a plurality-of compartments each containing one of a plurality of target electrodes arranged concentrically around an elongated cathode. Each of the target elec trodes is associated with a corresponding spade electrode used for locking the cathode ray beam in position upon its target electrode in a selected compartment. A mag netic field is created substantially parallel to the elongated cathode throughout the tube so that an electron beam formed at the'cathode of the tube will tend to follow a substantially equipotential path. For this reason the tubes are known as magnetron beam switching tubes. Meansare provided including the spade electrodes to create an electrostaticfield to establish a substantially equi potential line from a particular target electrode to the cathode'so that the electron beam will flow from the cathode to a single compartment defined by the said particular target. A small portion of the electron beam locks upon the associated spade electrode and reduces its potential by means of a load impedance to thereby direct the remainder of the electron beam upon the corre- .sponding target electrode.

Because of the magnetic held, the electron beam has a tendency to continuously rotate in a tight spiral around the cathode in one direction and would re-enter the cathode if it were not locked upon a particular spade electrode. When a substantially equipotential line is created between the cathode and one of the targets a beam is formed. It the beam is formed in one compartment and the equipotential line is directed to that compartment'adjacent to the compartment upon which'the electron beam is impinging, the electron beam is caused to advance to the said adjacent compartment where it looks upon the spade electrode thereof. In some of the earlier: tubes of this type, the locking action may be accomplished by lowering the potential of either the spade electrode 'or thetarget electrode. This type of tube is described inthe U. S. Patent 2,591,997 issued to N. E. G. Backmark. A more recent development has resulted in the provision of a switching or control grid electrode in each compartment. Such tubes are described in the U. S. Patent 2 ,721,955, of Sin-pih P an and Saul Kuchinsky, issued Octob'er 25,1955. The switching electrode of one compartment is maintained at a positive potential, and upon being reduced sufficiently in potential, pe'rforms the function of establishing an equipotential path between-the cathode and a spade electrode of an adjacent compartment to cause the electron beam to switch across the spa'de electrode and become locked in the adjacent compartment. If the potentials of successive ones of said'switching electrodes are caused to assume a potential such-as to establish an equipotential path between the associated compartment and the cathode, the

Patented May 28, 1957 electron beam will be caused to step consecutively from one compartment to the next. This has been accomplished in one manner by connecting one set of alternate switching electrodes (hereinafter referred to as even numbered electrodes) to one output terminal of a circuit such as a flip-flop or binary circuit and connecting the other set of (odd numbered) alternate switching electrodes to 'the other output of the flip-flop or binary circuit. Successive output pulses from the flip-lop circuit would then cause the electron beam to advance progressively from one compartment to the next.

It has also been known in the prior art that the beam may be switched from one target toanother by means of lowering the potential of the individual spade electrodes. This type of switching is described in the above mentioned Backmark'patent. Although highly successful for use in systems which progress from one beam position to the next, this method of switching is not in general de- 'magnetic field which causes the beam to step in only one direction. Therefore, thebeam may see a change in spade potential only for three or four positions in the direction it would normally advance underthe influence of the magnetic beam. If a reset is attempted to a position ninepositions removed from the existing beam position in a ten position tube, although it would only require switching to an adjacent compartment in a direction contrary to the normal rotation of the beam, the change in potential of one spade would not cause the beam position to change. Accordingly, it is desirable to produce a reliable means and method for causing the beam to step from any of its various positions to a selected reset position such as a 0 position in a decade counter tube.

A general object of the invention is to provide improved electronic reset circuits for beam switching tubes of the type described hereinbefore.

An object of the present invention is to provide a system including a multiple position electron beam tube in which the electron beam may be caused to step reliably from any of its various positions to a reset position in response to pulses applied to a single input terminal.

Another object of the invention is to provide a magnetron type electron beam switching tube system in which both clearing and reset may be accomplished by a single input signal.

In accordance with the'invention, therefore, the beam is first cleared and then reformed, upon a particular spade. This is done in a single operation by providing circuit embodiments which operate in response to a single signal produced by a manual reset switch, or equivalent electronic switching device responsive to elecironic pulses, to both reduce the potential momentarily on all the spades simultaneously, and to delay the return of the selected reset spade to normal potential until after the remaining spade electrodes have returned to normal potential so that the beam will be reformed upon that particular beam position designated by the selected spade. In this manner, the beam may be switched from any of its resident positions to the reset position because of the clearing operation immediately preceding the reset. The manner of resetting'the beam as described in connection with the hereinafter proposed specific embodiments of the invention efiects reliable reformation of the beam in a time'period compatible with the normal switching of the beam from one positionto the next so that a reset of the beam 'from any of its various positions to the reset position may not substantially slow down counting or switching operations performed by the tube.

Other objects and features of the invention will be electrodes.

more fully understood from the following detailed description thereof when read in conjunction with the drawings, in which:

Fig. 1 is a perspective assembly view, partly in section,

. of a multi-position magnetron beam switching tube utilized .in accordance with this invention. This type tube is well known in the art, as evidenced by descriptions in publica- -tions suchas Electronic Design for January 1954. Consequently only a brief description will be given herein of the structure and theory of operation of the tube 9 of Fig. '1. The cathode 41 is positioned Within the hermetically sealed envelope 10. Aplurality of elongated spade electrodes 31 through 40, having a U-shaped cross section, are positioned concentrically about the cathode 41 in spaced apart relation to one another. In the structure shown in Fig. 1, there are ten such spade electrodes.

Similarly, there are ten elongated target electrodes 11 through 20, having an L-shaped cross section, surrounding the spade electrode in a circular row centered on the cathode 41, and each associated with one of the ten spade Each target with its two adjacent spades defines a compartment for receiving the beam in one of its ten stable locked in positions. Ten switching electrodes 21 through are also positioned concentrically around the cathode 41 and are each individually positioned in one of the compartments between the open end of a target electrode and one extending leg of a spade electrode. For example, switching electrode 21 is positioned between the extending leg of spade electrode and the open end of target electrode 11. The concentric magnet 42 placed about the envelope 10 produces a magnetic field in the tube that is substantially parallel to the elongated cathode 41. This magnetic field is of a polarity which will cause an electron beam extending outwardly from the cathode 41 to sweep around the tube in a clockwise direction (viewed from the top of the tube) in accordance with well known principles. a

Each of the spade electrodes is adapted to lock the electron beam in a particular compartment by a lowering of its potential. The beam remains locked in by means of the electron beam flowing through a spade impedance connected to the particular spade electrode upon which 1 I the electron beam is impinging thereby causing enough potential drop across said impedance to establish a substantially equipotential pathsomewhere between the two adjacent spade electrodes and the cathode, thereby causing the beam to impinge upon the interposed target electrode. The switching electrodes perform the function of causing the electron beam to impinge upon the next consecutive spade electrode by distorting the electric field within a particular compartment to cause the electron beam to advance to that spade electrode which will hold the beam in the compartment adjacent tothe one upon which it impinges in the absence of a switching potential. It is to be noted that when the electron beam is directed to a compartment that the electron beam is actually impinging upon both the spade electrode and the target electrode. The target electrodes normally receive most of the electron beam since only a small portion thereof is required to lock the electron beam upona particular spade electrode.

The tube of Fig. '1 is a particular preferred embodiment of a magnetic type beam switching tube which may be used in accordance with the invention, and othertypes of switching tubes may likewise be used without distinguishing from the spirit or scope of the invention. In order to aiford a comparison of the schematic circuits of following figures with the heretofore described tube construction, like reference characters Will be used throughout the remaining figures of the drawing. In addition, the various elements of the tube are presented hereinafter in a different manner in order to make the functional operation of the drawing more easily understood. Thus, the electrodes of Fig. 2 are arranged in a straight line, and connections are made diagrammatically from theschematic switching circuit to the corresponding sets of even and odd grid electrodes of the tube which are shown respectively as open and filled circles.

In the embodiment of Fig. 2, the coupling" circuit 50, shown in left portion of Fig. 2, is utilized for stepping the beam from one target position to the next, and is connected in the conventional manner described in theabove mentioned copending application to provide alternate switching signals to the corresponding groups of even and oddgrid electrodes. Thus,'should terminals 51 and 52 be coupled to corresponding output terminals of a binary counter or flip-flop circuit, they would serve to reduce the voltage of the corresponding grid circuits from their normal +30 volts to substantially cathode potential 'and thereby move the beam to an adjacent compartment. In each compartment there is a group of three electrodes, such as in the "0 compartment, the target 20, switching electrode 3t) and spade 44). Thus, as the electron beam impinges upon the target 2%) it produces an output signal at the 0 target terminfl and causes enough beam current to flow upon spade 40 to cause a potential drop in flowing through the spade resistors 53, 54 and 55 to retain the spade 40 at a lower potential than spades 39 through 31. This occurs because spades 31 through 39, which include individual resistors 56 of substantially the same value as the combined resistance of resistors 53, 54 and 55, are not passing beam current. However, as the beam is stepped to a new position, say upon target electrode 19, the beam current will flow through resistor 56 and thereby reduce the potential upon spade 39 and cause the beam to be locked into position on target 19.

If it is assumed that the beam is impinging upon target electrode 19, the next input switching pulse would be at the odd switching input electrode 51 which causes the beam to fan out upon spade 38 and therefore advance to target electrode 18. Thus, the normal direction of advance of the beam is along the tube from compartments 0 through 9 successively and automatically back to 0 because of the coaxial arrangement of the tube electrodes as shown in Fig. 1. If desired, the spade resistor 56" coupled with the 9 position spade 31 may be made smaller in value so that the beam will not be stable and will clear or collapse automatically upon reaching a 9 count. In this event the beam may be reformed in the 0 compartment by an input potential at spade electrode 40 as applied to the terminal 58 located between resistors 53 and 54. This input potential could be taken directly from a target electrode of a preceding tube to provide a decade counter arrangement.

- Should it be necessary to reset the tube manually, however, the switch contact 60 is provided. Obviously this may be any equivalent switch device such as an electronic tube or gating circuit which couples the clearing and zero setting lead 61 to ground or cathode potential. By closing the switch 60, current is caused to flow from the 150 volts spade potential terminal Es through a resistor ,64 commonly connected with all the spades 31 through 40 at the bus 65. This current flow caused by grounding lead 61 willresult in reduction of the spade potentials to such an extent that the beam is dislodged from the .locked'in target position. In this respect the beam is at least partially extinguished so that it may be reformed upon the 0 spade electrode 40. The reduced spade potential is'mornentarily applied by holding down the switch "60 manually or by a corresponding electronic pulse upon terminal '61 of suificient duration to clear the tube by extinguishing the beam from its locked in target position.

As the switchj60 is rel'e iasedthereby ungrounding lead '61, the spades 3 1'thi'oug'h warmest immediately return t'o'the Ovolt spade potential-of terminal E5, since no beam current is flowing at this time through resistor 6'51. However, capacitor68 is connected to shunt resistor'55 coupled between zero-trauma 61 and the common bus'65to cause the'sp'ade40 to remain at reduced potential anemia spades 31through; 39 are returned to their normal spade'p otentials Accordingly, the necessfary' equipote'ritialp'a'th is'established to reform the beam tothe target'Zt). Thus, the'capacitor68 is chosen to maintain the lowered'p'otentialupon spad'e'dil long enough for thebearntoreforfn' in the locked in position'on target 20.

A bypass" capacitor '69niay be"provided in shunt with resistor '64 ifne ces'sary to reduce any tendency for degenerati'on action of resistor during the clear and reset switching eab'd, This degeneration is desirable in normal tube operation because changes of spade potential will thereby have less efiect on tube operation as described an'd clai'riied' inthe cop ending application of J. Forman, Serial No. 574,478, filed March 28, 1956, and assigned tothe same assignee as the present application. However, the'tende'ncyto degenerate during the switching andreset period "would'tend' to'inipede the clearing and resetting function. Thus, consider the'effect of resistor 64 asbea'rn currentbegins toflow'to'the reset spade electrode after switchtl is'open'ed. Beam current will cause the spade supply 'potentiakto 'be' reduced which will thereby tend to reduce the potential of all the spades simultaneously and thereby tend to prevent reformation of the beam. However, capacitor 69 will serve to bypass the initial surge of beam current and thus eliminate the tendency for degeneration and permit the beam to be more reliably formed upon target 20. The time constant R55 C68 should exceed that of R64 C69 for proper operation.

Although it is obvious that various parameters may be used in connection with the invention, a range of typical values is shown in the following chart for the purpose of enabling those skilled in the art to better under stand the nature of the invention and to find suitable parameters for employing it in other specific circuit environments, or with tubes having difierent characteristics than the described tube, which is a standard MOl0-6700 type tube formerly supplied by Haydu Brothers of New Jersey, now the Electronic Tube Division of Burroughs Corporation. The corresponding values of the various accompanying components are as follows:

In operation, therefore, it is evident that the structure of Fig. 2 serves to simultaneously reduce the potential upon all of the spade electrodes to clear the beam, while a momentary clear signal is utilized to ground lead 61 to cathode potential. The reformation of the beam on target in the 0 compartment is performed also with the clearing signal by action of capacitor 68 in delaying the return of spade 40 to the normal spade potential of 150 volts until after the beam is formed in compartment 0 thereby causing the beam to lock in by beam current flow through the series resistors 53, 54 and 55.

Other embodiments oftheinvention maybe constructed to operate ina similarrnanner such as, for example, the enibodinient of Fig. 3. As seen from this embodiment the cathode "41 of the beam switching tube need not be grounded, and the common resistor necessary to reduce the spade t o cathode potential upon the closing of switch 60 'may be incorporated in the cathode to ground path of the tube. It is obviousin operation of this device to have the voltage divider action of resistors 55 and 64 as switch60 is closed serve to reduce the spade to cathode'potential in the same manner as the voltage divider action of Fig. Zhhdthieby extinguish the beam. Likewise, the time constant provided by the shunt resistor 55 and capacitor 68 will s'e'rvetoretain spade 40 in its lowered potential condition l'oii'g enough topermit the beam to be reformed in the O compartment.

A still further embodimentof the invention is evident from considerationbf Fig. 4 wherein the beam may be extinguished by opening the cathode circuit with reset switch 60. The rlay'9't) is coupled in the common beam 'ciir'reiitpath and returned to the +150 volt operating potential terminal 91 so that it'o p er'1s'its single set of contests 92 when beam cur'r'e'iit flows. The contact 92 is noriiially closed to r et'ain th'e" spade 40m ground or cathode potential. Thus, by opening {switch 60' the beam is k tiriguis'hed, thereby de -e nergiiing relay 9% to lower spade potentialdil. Thereafter as thecontact 60' is re closed the beam is reformed and upon the 0 compartneat containing the l'owe're'dpotential spade 40 to thereby 're-establishbeamcurrent through relay and open switch 92 fo'r'nb1 alsteppin g operation of the tube.

"lCh'especific manner of ernp'loying electronic reset sigrials in"the" place of a manual switch 6 0 is shown in the embodiments of Figs. 5 and 6. Thus, Fig. 5 illustrates a direct current coupled high speed triode circuit operable with pulse widths of about one microsecond. The circuit may be used to replace the switch 60 hereinbefore described in connection with Fig. 2.

Likewise the blocking oscillator type of circuit shown in Fig. 6 may be used for alternating current coupling to the lead line 61 of the reset circuit in Fig. 2. This circuit assures that the clearing and reset operation is accomplished in a minimum time period approaching one microsecond even though the input pulse is shorter or longer than the switching pulse. Thus, if AT is the width of the input pulse and T is the spacing between two consecutive pulses, the circuit will reliably operate to reset under the conditions .1 .sAT .8T, which signifies that the input pulse I width AT may be anywhere between the lirnits of one tenth microsecond and eight tenths of the spacing between two consecutive pulses. The circuit values of the circuits of Figs. 5 and 6 are shown on the drawing and the turns ratio of the transformer in Fig. 6.

It is obvious from these embodiments that applicant has produced an improved manner of resetting the beam. Accordingly, those novel features believed to define the nature and scope of his invention are presented in the accompanying claims.

What is claimed is:

1. The method of resetting a multi-position magnetron beam switching tube having encompassed within its magnetic field a plurality of target and corresponding beam forming spade electrodes to a selected position comprising the steps of operating all the spade electrodes at a substantially identical positive potential, reducing the potential of one spade to form a beam on the corresponding target, simultaneously lowering the potential of all the spade electrodes enough to cause the beam to be cut-off and thereby removed from the target upon which it resides, restoring said positive potential to all the spade electrodes, and delaying the return of the potential of the spade of said selected position to said positive potential beyond the return of the remaining spade electrodes, whereby the beam is reformed to said selected position.

2. A circuit comprising in combination, a magnetron beam position tube having a cathode and a plurality of target and corresponding beamrforming spade electrodes, a circuit for applying a potential to all of said spades positive with respect to said cathode, means for selectively switching the beam from target to target, individual resistors in said circuit for each spade of such value that the beam is locked in position as it impinges upon each target in response to beam current flowing to the corresponding spade, clearing means for momentarily lowering the potential to all of the spades simultaneously, and reset means cooperativelyoperative with the clearing means to delay the return of one designated spade to said positive potential'with respect to the remaining spades upon termination of the lowering of potential by the clearing means.

3. In combination, a magnetron beam position tube having a cathode and -a plurality of target electrodes each with a corresponding beam forming spade electrode, a positive spade potential source having a negative terminal connected with said cathode, individual resistances connecting each spade to the positive terminal of said source and having a value sufficient to hold the beam in a stable locked in position upon a corresponding target of any spade, a common resistor coupled in the spade beam current path, selectively operable momentary switching means connected between said cathode and the resistance of one spade electrode, whereby operation of the switching means serves to reduce the potential of all spades by current flow through said common resistor in sufficient magnitude to at least partially extinguish the beam and thereby to dislodge the beam from a locked-in position, and a capacitor coupled to the individual resistance of said one'spade electrode'to delay the return of potential of said' one spade electrode to said positive spade potential, whereby the beam is reformed upon said one spade electroderand the corresponding target electrode.

4 A combination as defined in claim 3 wherein the common resistor is connected in series between the tube cathode andsaid negative spade potential source terminal; a

5. A combination as defined in claim 3 wherein the common resistor is connected in series between the tube spades and said positive spade potential source.

6 In a system employing a magnetron beam switching tube with a cathode and'a' plurality of target and corresponding beam forming spade electrodes, a combination clear and reset circuit comprising means for operating all of said spade electrodes at a normal positive po- :tential, means for reducing the potential of one spade in response to beam current,-clearing means for momentarily reducing the spade to cathode potential, and reset means for retaining the last mentioned reduced potential on afselected spade electrode for a longer time period than on the remaining spade electrodes.

References Cited in the file of this patent UNITED STATES PATENTS Fan et a1. Oct. 25, 1955 

